Energy storage apparatuses including an outer housing that houses a plurality of battery cells are well known. An example of such an energy storage apparatus is disclosed in Patent Literature 1 (Japanese Patent No. 4638528). The outer housing in such energy storage apparatuses forms a housing space for housing the battery cells and includes an opening. The outer housing is typically a six-sided, box-shaped component having the opening in place of one of the six sides. More specifically, the outer housing has four side walls extending from and perpendicular to a rectangular bottom surface.